Interlocking concrete blocks are used for many outdoor construction applications, one of the most common being the construction of retaining walls. Interlocking concrete blocks are thus designed for durability, stability and aesthetic appeal.
One of the ways that aesthetic appeal is imparted to a structure formed from interlocking concrete blocks is to make the exposed face look as much as possible like natural stone. Conventionally this is accomplished by casting concrete blocks in a mold, with the exposed face of one block joined to the exposed face of another block, and breaking the blocks apart along a score line. This results in an essentially random topography on each exposed face of the block pair, which produces a natural ‘look and feel’. An example of a conventionally-formed interlocking concrete block is illustrated in FIG. 1L.
For example, FIGS. 1A to 1L illustrate a typical molding process for a prior art interlocking concrete block 20. FIG. 1A shows a prior art mold 10 with a mold box 12 and a floor comprising a draw plate 14 in position for casting. The draw plate 14 has a profile with projecting features 5a designed to form the interlocking structures on the bottom of the block 20 (in the embodiment shown recesses 5) and projecting features 6a forming break lines 6, as shown in FIG. 1B. After dry mix concrete has been fed into the mold 10, shown in FIG. 1C, a press head 15 is actuated to consolidate the concrete 1. In the prior art blocks 20 shown the press head 15 also forms the top interlocking structures, ribs or “tongues” 4 complementary to the recesses 5, and break lines 6, as shown in FIG. 1C.
The steps in the prior art forming process are illustrated in FIGS. 1D to 1L. The mold box 12 is positioned (FIG. 1D) beneath the press head 15 and the mold box 12 is placed on the draw plate 14 (FIG. 1E). Concrete 1 is fed into the mold 10 (FIG. 1F) and the press head 15 is actuated to consolidate the concrete and form the top surface 22 of the block 20 (FIG. 1G), then the press head 15 is retracted (FIG. 1H). The draw plate 14 can be removed immediately due to the zero slump concrete mix and the consolidation by the press head (FIG. 1I), and the mold box 12 lifted off of the slab of joined blocks 20 (FIG. 1J), leaving the unbroken slab of blocks 20 on a board or pallet (not shown). After the concrete has cured for at least 12 hours, blades 7 are forcibly applied to the break lines to split the individual blocks 20 from the slab (FIG. 1K). The exposed faces of the blocks 20 manufactured in this fashion have a “split block” finish, shown in FIG. 1L, which has been an industry standard for over 25 years.
There are disadvantages to this manufacturing method. While the (complementary) topographies produced on the exposed faces by breaking the blocks apart looks natural, using this manufacturing method the manufacturer has no control over the final appearance of the exposed face of the block because the fracturing occurs randomly. This limits the profile of the exposed face, and occasionally blocks must be rejected because of over-breakage resulting in the exposed face having a damaged appearance. Also, the height of the concrete blocks is determined by the stroke of the press head, which is a moving part, and since the length of each stroke of the press head may be slightly different there is a commensurate variation in the heights of concrete blocks cast at different times. Furthermore, if a colour other than natural concrete is desired on the exposed face, the colour must be mixed into the entire volume of concrete so that the exposed face provides a uniform colour, which given the cost of some dyes can be very expensive.
One or more of the embodiments of the invention addresses one or more of these disadvantages. While embodiments of the invention are described in detail below, it will be appreciated that not every advantage of the present invention necessarily applies to every embodiment described or claimed herein.